Macadamia nuts are white seeds or shelled kernels from an evergreen Australian native tree Macadamia spp. especially integrifolia or tetraphylla belonging to the family Proteaceae. They are increasingly being used in the form of dried and roasted nuts in food due to its unique flavors, multipurpose uses and long shelf life. Macadamia nut allergy is less common than other tree nut allergies, but it is included in the collection of nine nuts that accounts for the majority of the tree nut allergies globally. The prevalence of the tree nut allergy including macadamia varies according to region, age and diagnostic definition in different countries. Cases of oral ingestion of macadamia nut have been reported to cause allergic reactions ranging from pollen food allergy syndrome to severe reactions like anaphylaxis. There is a paucity of information on corresponding allergens which may be seed storage proteins. Macadamia nuts are found to be cross-reactive to other tree nuts like hazelnuts, walnuts, cashew nuts, or pecan nuts with co-existent allergies. The only effective approach for this allergy is to avoid the consumption of tree nuts or food products containing them. 

Worldwide distribution

Macadamia nut allergy is less common than other tree nut allergies. It is reported to be <5% in tree nut allergic individuals in the US. However, certain case reports of macadamia nut allergic reactions ranging from pollen food allergy syndrome to severe reactions are present (10, 11).

Macadamia was responsible for allergy in only 14 out of 122 nut allergic participants in a study in the UK where the consumption of macadamia nuts was 1% (12). A review evaluated the prevalence of tree nut allergies to nine specific tree nuts i.e. walnuts, almond, pistachio, cashew, pecan, hazelnut, Brazil nut, pine nut and macadamia nut. The prevalence of tree nut allergies including macadamia in Europe, confirmed by oral challenge, was found to be ranging from 0 to 4.3%. These studies were mainly including children with only one study in adults. The US-prevalence data showed 0.5% in adults and 1.1% in children based on telephone surveys while Canada showed a prevalence of 1.7% in children and 1% in adults. Australia reported a prevalence of 2.3% in school children of 10-14 years old while 0.32%, 0.28% and 0.3% were reported in Korean, Philippines and Singapore school children respectively. This confirms that tree nut allergy including macadamia varies according to region, age and diagnostic definition (10).

The use and demand for macadamia nuts are increasing throughout the world due to their unique flavors, multipurpose uses and long shelf life (1, 7).

Worldwide distribution

Macadamia tree is considered to be an Australian native nut crop (1) belonging to the family Proteaceae. It has its origin in rainforests of North-East Australia as wild progeny and considered to have been spread globally to places outside its natural habitat, like Hawaii, Southwest Australia and South Africa where it is an important economic and commercial crop (6, 7). The use of the macadamia kernels in the diet has expanded with currently being Australia, South Africa, Kenya, and United States the largest producers together with cultivation in other countries like China, Southeast Asia, South America, Malawi, and New Zealand (7). The white kernels of the macadamia nuts are widely consumed as dried, roasted in oil or salted. Macadamia nuts are also used in baked goods like cakes and cookies, as well as, ice-cream (5, 10). 

Main

Oral ingestion of macadamia nuts can trigger oral food allergy or anaphylaxis like symptoms (13-15). Fresh macadamia nut is thought to be responsible for allergic responses (5, 13, 14).

Systemic IgE-mediated reactions

Macadamia nut allergy report symptoms ranging from oral allergy syndrome to severe reactions (10). Certain cases have reported macadamia nut allergy as anaphylaxis or severe symptoms (2, 11). 

Severe reactions like generalized pruritis, throat itching, rhinitis, dyspnoea, dizziness, severe oral burning, and swelling were seen in two cases of 42-year and 34-year old males. Cases of anaphylaxis were also reported presenting as severe erythema, generalized urticaria, tongue and throat swelling, swelling in the eyes, dyspnoea, wheezing and hypotonic circulatory reaction along with severe erythema and periorbital angioedema in 1-year old (13, 14, 16).    

Prevention strategies

Avoidance

Tree nut allergies usually develop during childhood but are considered to be life-long (17) and the likelihood of its resolution is only about 10% (10). The only effective approach to this date is avoiding the consumption of tree nuts or food products containing them (10, 17). Due to this, USFDA and European Union have made it mandatory to mention allergenic substances on the food label which included tree nuts like macadamia too (3, 17, 18).

Allergenic molecules

Most commonly, the allergic proteins in nuts are found to be seed storage proteins (18). But so far, no allergenic proteins have been characterized from M. integrifolia or M. tetraphylla or their hybrids. Low IgE reactivity to proteins with 17kDa and 12kDa, present in macadamia nut oil has been reported from sera of macadamia nut allergic patients (2, 11). Also, Herbst, Wahl (16) has reported another protein of 45 kDa as a potential macadamia allergen. However, Rost, Muralidharan (11) in an attempt to identify macadamia nut allergens, demonstrated that storage proteins belonging to 11S globulins and 7S vicilins in macadamia nuts share homology with sesame and walnut allergens. Other proteins like enolase 2 and its isoform 1 rubber tree latex allergens and peptidyl-prolyl cis-trans isomerase 1 birch pollen allergen, Bet v 7, matched with 90% identity (11).

It is also shown that roasted and raw macadamia nuts have shown IgE reactivity to 17 kDa protein (2). 

Cross-reactivity

Macadamia nuts are found to be cross-reactive to other tree nuts like hazelnuts, walnuts or pecan nuts with co-existent allergies (12, 19). The probable allergen responsible for cross-reactivity with hazelnut is thought to be a 17 kDa protein (2, 11). Cross-reactivity with cashew nuts has also been described (20). Usually, patients with peanut allergy are advised to avoid all tree nuts due to cross-reactivity. However, 97% of peanut-allergic patients depicted a negative skin prick test with macadamia (21). A recent retrospective study in the Midwestern United States found that a high rate of co-sensitization (77%) exists between macadamia tree nuts and coconut (22).

Author: Turacoz Healthcare Solutions

Reviewer: Dr. Christian Fischer

Last reviewed: November 2020